<p>Developers typically measure a Web application?s quality of service in terms ofresponse time, throughput, and availability. Poor QoS translates into frustrated customers, which can lead to lost business opportunities. At the same time, company expenditures on a Web site?s IT infrastructure are a function of the site?s expectedtraffic. Ideally, you want to spend enough, and no more, allocating resources where they?ll generate the most benefit. For example, you shouldn?t upgrade your Web servers if customers experience most delays in the database server or load balancer. Thus, to maximize your ROI, you must determine when and how to upgrade IT infrastructure.</p>